An antenna is an essential component to provide communication and broadcasting services and specifically, a dual reflector antenna having high directivity is mainly used thereof. The dual reflector antenna has a structure in which the directivity is improved using a subreflector in addition to a main reflector (parabola).
A subreflector of the dual reflector antenna generally has an elliptical or hyperbolic shape having two focal points. A first focal point which is one of the focal points of the subreflector is coincident with a focal point of a parabolic reflector and a second focal point which is the other focal point is coincident with a phase center of a feeding element.
When a signal flow in a transmitting mode is examined, a signal which starts from a phase center (the second focal point) of the feeding element is reflected from the subreflector to proceed toward the first focal point of the subreflector. This signal proceeds on an aperture of the antenna as an in-phase planar wave. In the receiving mode, contrary to the transmitting mode, the signal which starts as the planar wave passes the first focal point of the subreflector and proceeds to the phase center of the feeding element.
Generally, an antenna which satisfies high directivity and low side lobe level is evaluated to have good performance. Therefore, in order to achieve high directivity, radio wave interference caused by the subreflector needs to be reduced and in order to achieve the low side lobe level, a diffracted wave at a corner of the reflector needs to be reduced.
In the related art, in order to simultaneously satisfy the high directivity and the low side lobe level, the main reflector and the subreflector are simultaneously molded through complex calculation for field distribution or a ray or corrugation is provided on a surface of the subreflector to concentrate the signal and the diffracted signal is reduced through an external choke.
However, according to the related art, complex calculation is necessary or a separate device needs to be added, which results in more cost and time to design an antenna.